Research On Damage Detection Technology Based On FBG And Acoustic Wave Technology

Damage detection is one of the most important industrial technologies,which is of great significance to the development of society and economy and the safety of people and property.At present,it develops towards the integration of multi sensor technology,and the combination of fiber bragg gratings(FBG)and acoustic wave technology is one of the hot spots in the current damage detection technology.In this paper,we measured ultrasonic carrying the damage information in the structure based on FBG,and construct a photoacoustic detection system to detect damage.The main works are as follows.(1)It analyzed the research progress of ultrasonic technology,FBG used in structural health detection technology and FBG demodulation technology.(2)It analyzed the characteristics of ultrasonic field distribution and determined FBG should be arranged axially;analyzed the principle of FBG and the influence of the length of FBG on the reflection spectrum under ultrasonic excitation;obtain the relationship between the length of FBG and the ultrasonic wavelength.(3)In order to solve the problem of wavelength demodulation when FBG was used to detect high frequency acoustic signal,a FBG high-frequency demodulation system was designed based on a long-period fiber grating(LPFG).In the system,the FBG's reflected light intensity was modulated by LPFG,and the ultrasonic signal can been detected from the change of the output light intensity.The experimental results show that the system can detect the high amplitude ultrasonic,but the sensitivity is too low to obtain the low amplitude Lamb wave signal.(4)To acquire a high sensitivity wavelength demodulation system,an improved demodulation system was studied based on narrow reflection spectrum FBG,by which the broadband light was modulated into a narrowband light source.The sensing FBG was used to modulate the narrowband light source,and the ultrasonic signal was obtained by detecting the reflected light intensity of the sensing FBG.The experimental results show that the improved system's demodulation frequency reaches 100 KHz and the Lamb wave signal is acquired.The demodulation system demodulation range for a sensing FBG is small,but the system can meet the requirements because of the sensing FBG center wavelength shift is very small excited by Lamb waves.Through designing corresponding narrowband FBG,multiple sensing FBG can be demodulated.In addition,considering the narrowband light source in the system is modulated by a broadband light source,the cost reduces a lot.(5)At last,a structural health monitoring system based on FBG and sonic technology was constructed.We used distributed measurement system to identify and locate and damage identification and localization based on amplitude method on a composite plate.And the experimental results show that the system is successful.